At a small event in Hamburg, Matthias Bolliger practically demonstrated the technology and possibilities of HDR.
»High Dynamic Range (HDR) is a process that achieves a greater range of contrast compared to Standard Dynamic Range (SDR). Here, lighter and darker areas of the image are displayed more precisely, which enables a more realistic reproduction of colors and brightness« – at least that’s what ChatGPT says if you ask this AI tool (— the encyclopedia of film-tv-video.de already says more inside).
This scratching at the surface shows that it ultimately takes a lot more than a computer or cell phone and AI to really explain and understand things. You have to see them — especially in the case of HDR — and have them explained in a practical way.
Under this premise, the camera rental company Cine-Mobil, the Post-Haus Optical Art and the film and theater equipment FTA organized an event for filmmakers in Hamburg at the beginning of February in order to, on the one hand, “everyone around one table” again after the Corona hole. to exchange ideas and, above all, to bring HDR closer to all those interested in the industry in a practical way.
Matthias Bolliger was won for this, a renowned cameraman who was behind the camera for films such as “Chiko”, “Blutzbrüdaz”, various “Tatorte” and the series “4Blocks” and has already received numerous awards. He also passes on his practical knowledge as a lecturer and trainer, which in turn led to the current event.
In the FTA halls, Bolliger had already filmed various demo recordings with an Arri Alexa 35 (info) before the event. The assembled set could be viewed live at the event, and you could try out HDR looks yourself with the camera. A mobile grading suite from Optical Art was also available. So there’s a lot of incentive to make your way to the west of Hamburg.
Many of the guests already had points of contact with HDR, after all, almost every reasonably modern camera can somehow also record in HDR. But how does HDR work in film and video, how to go deeper into this buzzword?
Basics
HDR has been known in photography for a long time. Here it is much easier, at least with still subjects – snap several photos with different exposures and then stack them to an extremely high-contrast end product. In this way, shadows and lights in particular as well as the color intensity can be optimized, and the image has a higher dynamic range.
With video, things are a little different. A prerequisite for HDR is the highest possible color sampling, and at least in 10 bit and 4:2:2. If you then switch your camera to HDR, you will suddenly find yourself in a new color space – Rec.709 is simply far too small for HDR. And this new color space is called Rec.2020 or BT.2020.
The camera is of course only one end of HDR, so you need a sensor and signal processing that can capture, process and store an HDR signal. The other side is the display: you obviously also need displays that make it possible to display HDR images, otherwise a lot of the effort and effort that you put in at the front end doesn’t make it through to the back end of the chain.
An important term that is often used in HDR in the display area is nits. This measures the short-term maximum luminance of a display. So, the higher the number of nits, the better the screen’s ability to display HDR content with a wider brightness range and higher contrast. A nit equals one candela per square meter, so it’s a unit for measuring luminance.
Between the camera and the display you need signal formats that can transport the content digitally from one end to the other. There are various HDR formats that make this possible. Several methods and manufacturers compete in the market to find out what the best HDR format is. Different technologies and specifications are used in each case. The most common HDR formats at a glance:
HDR10 is an open HDR format widely used on Blu-ray and streaming platforms. It uses a consistent dynamic range/color palette for all devices and can display a maximum of 1,000 nits.
HDR10+ is a further development and goes up to 4,000 nits.
Dolby Vision: A proprietary HDR format that offers higher resolution and greater color depth at 12-bit than HDR10. It can make device- and content-specific adjustments to enable optimal playback. In addition, the maximum brightness is 10,000 nits.
HLG (Hybrid Log-Gamma) is an HDR format developed for the transmission of HDR content over regular SDR transmission channels. It can be played on a variety of devices, including TVs, monitors, and projectors. The big advantage of HLG is that the broadcaster can broadcast a single video signal, which is then automatically displayed in HDR or SDR, depending on the end device, depending on what the device can do.
For optimal playback, the player should support the same HDR format that the supplier used. Otherwise there is transcoding within the chain — and that actually always costs image quality.
Praxis
In the history of film technology there have always been surges in innovation, but these have not been able to establish themselves on a broad basis in practice: Stereo 3D was ultimately reinvented three times…
When it comes to innovations, the question is always whether they will catch on. And unlike stereo 3D, it looks very good in HDR — simply because you can see it very clearly with the unaided naked eye — and it makes sense.
In addition to all the technical details and workflows, Matthias Bolliger highlighted an aspect in his presentation that many do not even think about when it comes to HDR: the sensible distribution of the brightness values and use of the headroom. Of course you can make your picture pop and pop and stretch the signal up and down to the maximum. But that may not be the main benefit of HDR…
To clarify, you can use an analogy and take the sound mastering in a timeline: Of course, when I’m editing a horror film, I want to shock the viewer with loud noises. Therefore, the level of the whole film is leveled down — or at least a few passages before the shock event, in order to have some room for the acoustic shock effects without overdriving. In practice, of course, the viewer sets their television to the reduced volume. Now my audio effects come, of course, they are much louder and have a better effect.
Transferred to HDR, we also leave some headroom when grading. Matthias Bolliger was able to explain this to us very well in his lecture: An explosion and a flash will always be brighter than pure white in a normal picture.
In the example, in the RGB parade or in the waveform monitor, the white was not placed on the 1,000 nits upper limit of the display, but below it. This gives you more room to be able to show extremely luminous things like the explosion mentioned on the one hand brighter and on the other hand more detailed – because nothing burns out. With advancing technology, we will soon be really dazzled in the living room if there is a flash in the film…
Another advantage of HDR is the dynamic range that the light sources gain in the image. In practice, this means: more details and, above all, more dynamics in the colors. LEDs in particular benefit from this when they are used, for example, as a visible light in the image.
Since the set with which Matthias Bolliger shot the scenes was still set up on site, you could play with the exposure of the Arri Alexa 35 yourself and examine the result in the HDR preview monitor – which is of course mandatory when shooting in HDR.
In addition, Optical Art had brought a mobile grading suite, and Louise Temmesfeld was available for Techtalk after her presentation. The same goes for Matthias Bolliger, with whom you could once again exchange ideas about the camera and workflow.
Conclusion
Ultimately, that is what made the event so charming: Being able to talk shop in a relaxed environment, cultivate new and old friendships and also continue your education. In any case, for me personally, the event was an incentive to be even more open to HDR in terms of using it in future projects.
Matthias Bolliger made it clear that HDR can do much more than just bright colors. Here too, of course, it always depends on what you shoot. All productions should benefit from this, whether high or low key in the scenic area, realistic and glaring explosions in action films or simply the beauty of our nature with all its colors and contrasts, captured in a documentary.
